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Formula: Ce2(CO3)3.4H2O
Hydrated normal carbonate, cerium-bearing mineral
Crystal System: Orthorhombic
Specific gravity: 3.28 measured
Hardness: 2½
Colour: Pale yellow
Solubility: Effervesces strongly in cold dilute (1:5) hydrochloric acid (Mindat)
Weakly RADIOACTIVE
Environments
Calkinsite occurs in carbonate veins as a weathering product closely associated with
burbankite (Webmin).
Localities
At the Central Khanneshin deposit, Khanneshin complex, Reg District, Helmand, Afghanistan, calkinsite-(Ce) is associated with
dolomite, khanneshite,
carbocernaite,
mckelveyite-(Y),
baryte and chlorite
(HOM).
At the Vuoriyarvi alkaline-ultrabasic massif, Northern Karelia, Murmansk Oblast, Russia, calkinsite-(Ce) is associated with
baryte, strontianite and
pyrite
(HOM).
At the type locality, the Vermiculite prospect No. 6, Big Sandy Creek, Bearpaw Mountains, Hill county, Montana, USA, the mineral
deposits occur in shonkinite, mafic
monzonite and syenite.
Sanidine, biotite,
aegirine, calcite,
pyrite and pyrrhotite are the major minerals in
these deposits. At this locality, shonkinite is irregularly fractured and is host
to interconnecting veins, up to 8 inches thick. Calcite is the dominant mineral, and the
other minerals are burbankite, calkinsite-(Ce),
sanidine, biotite,
aegirine,
pyrrhotite, pyrite,
chalcopyrite, galena,
tetrahedrite, ilmenite,
baryte, ancylite and
lanthanite.
In unweathered specimens the veins are essentially burbankite intricately veined by very
fine grained ancylite and subordinate amounts of
calcite and biotite.
Burbankite is also disseminated in calcite
as anhedral crystals commonly less than 0.02 mm in size. As a result of weathering, the
burbankite-ancylite intergrowth is altered to
a porous, flaky, powdery material containing plates of calkinsite-(Ce), lanthanite,
fine-grained baryte, goethite, and some other
unidentified minerals. Calkinsite-(Ce) is most abundant in the partly altered area adjacent to unweathered
burbankite, and lanthanite and
baryte are most abundant in completely altered material. Both calkinsite-(Ce)
and baryte are present also in rare vugs that show no evidence of weathering. The plates of
calkinsite-(Ce) are less than 1 mm in size.
In the sequence of mineral development, burbankite is younger than most of the
calcite; ancylite was formed locally by a reaction
on burbankite by a hydrothermal solution. In this reaction
burbankite contributed to form a hydrous complex carbonate richer in rare earths. Both
of these complex carbonates were decomposed to form calkinsite-(Ce) and lanthanite.
This final decomposition most probably was caused by weathering, and further resulted in deposition of
baryte, goethite and an unidentified sulphate
(AM 38.1169-1183).
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